Technical Field
The present invention relates to a glass substrate and a method for manufacturing the same, a cover glass and a method for manufacturing the same, a personal digital assistant, and a display device.
Background Art
Recently, as an advanced security measure for electronic apparatuses, a method of using a fingerprint for personal authentication has been actively used. Examples of the fingerprint authentication method include an optical type sensor, a heat-sensitive type sensor, a pressure-sensitive type sensor, a capacitance type sensor and an ultrasonic type sensor. From the viewpoint of sensitivity and power consumption, a capacitance type sensor and an ultrasonic type sensor are considered to be excellent.
For example, when a detection object approaches or contacts a portion of a capacitance sensor, the capacitance sensor detects a change in the local capacitance of the portion. In a general capacitance sensor, the distance between an electrode arranged in the sensor and a detection object is measured based on the capacitance. In addition, an object to be detected can be detected three-dimensionally by using ultrasonic waves in the ultrasonic type sensor. In this type, the object to be detected can be detected through a foreign matter such as liquid, and this type is expected as a biometric sensor improved in security. A system with a fingerprint authentication function using such a sensor is small and lightweight and has low power consumption. Therefore, this system is mounted on a personal digital assistant (PDA) such as a smartphone, a mobile phone, or a tablet personal computer. Usually, in order to protect a fingerprint authentication sensor (hereinafter this maybe simply referred to as a sensor), a cover glass is arranged above the sensor.
In Patent Document 1, as a cover glass for a mobile device, a concave portion is formed in the main surface of the cover glass for realizing recognition of letters or figures by users. Here, when the haze value of the concave portion is 10% or more, the visibility of the concave portion is increased. In addition, the surface roughness Ra of the concave portion is made larger than the surface roughness Ra of the flat portion of the main surface. With that, owing to the difference in the feel between the concave portion and the flat portion of the main surface, the tactile in recognizing the concave portion is thereby enhanced.
Patent Document 2 discloses a method of manufacturing a cover glass for mobile devices. In the manufacturing method, a glass sheet is etched after a resist mask has been arranged thereon, and plural cover glasses for portable devices are thus extracted.    Patent Document 1: JP-A-2013-137383    Patent Document 2: JP-A-2013-1599